Diabetes is characterized by elevated levels of plasma glucose (hyperglycemia) in the fasting state or after administration of glucose during an oral glucose tolerance test. In type 1 diabetes, or insulin-dependent diabetes mellitus (IDDM), patients produce little or no insulin, the hormone which regulates glucose utilization. In Type 2 diabetes, or noninsulin-dependent diabetes mellitus (NIDDM), insulin is still produced by islet cells in the pancreas. Patients having Type 2 diabetes have a resistance to the effects of insulin in stimulating glucose and lipid metabolism in the main insulin-sensitive tissues, including muscle, liver and adipose tissues. These patients often have normal levels of insulin, and may have hyperinsulinemia (elevated plasma insulin levels), as they compensate for the reduced effectiveness of insulin by secreting increased amounts of insulin (Polonsky, Int. J. Obey. Relat. Metab. Disord. 24 Suppl 2:S29-31, 2000). Insulin resistance is not primarily caused by a diminished number of insulin receptors but rather by a post-insulin receptor binding defect that is not yet completely understood. This lack of responsiveness to insulin results in insufficient insulin-mediated activation of uptake, oxidation and storage of glucose in muscle, and inadequate insulin-mediated repression of lipolysis in adipose tissue and of glucose production and secretion in the liver. Eventually, a patient may be become diabetic due to the inability to properly compensate for insulin resistance. In humans, the beta cells within the pancreatic islets initially compensate for insulin resistance by increasing insulin output. The onset of Type 2 diabetes due to insufficient increases (or actual declines) in beta cell mass is apparently due to increased beta cell apoptosis relative to non-diabetic insulin resistant individuals (Butler et al., Diabetes 52:102-110, 2003).
Persistent or uncontrolled hyperglycemia is associated with increased and premature morbidity and mortality. Often abnormal glucose homeostasis is associated both directly and indirectly with obesity, hypertension, and alterations of the lipid, lipoprotein and apolipoprotein metabolism, as well as other metabolic and hemodynamic disease. Patients with Type 2 diabetes mellitus have a significantly increased risk of macrovascular and microvascular complications, including atherosclerosis, coronary heart disease, stroke, peripheral vascular disease, hypertension, nephropathy, neuropathy, and retinopathy. Therefore, effective therapeutic control of glucose homeostasis, lipid metabolism, obesity, and hypertension are critically important in the clinical management and treatment of diabetes mellitus.
Patients who have insulin resistance often exhibit several symptoms that together are referred to as syndrome X or metabolic syndrome. Patients with metabolic syndrome have an increased risk of developing atherosclerosis and coronary heart disease.
There are several available treatments for Type 2 diabetes, each of which has its own limitations and potential risks. Physical exercise and a reduction in dietary intake of calories often dramatically improve the diabetic condition and are the usual recommended first-line treatment of Type 2 diabetes and of pre-diabetic conditions associated with insulin resistance. Compliance with this treatment is generally very poor because of well-entrenched sedentary lifestyles and excess food consumption, especially of foods containing high amounts of fat and carbohydrates. Pharmacologic treatments for diabetes have largely focused on three areas of pathophysiology: (1) hepatic glucose production (biguanides, such as phenformin and metformin), (2) insulin resistance (PPAR agonists, such as rosiglitazone, troglitazone, engliazone, balaglitazone, MCC-555, netoglitazone, T-131, LY-300512, LY-818 and pioglitazone), (3) insulin secretion (sulfonylureas, such as tolbutamide, glipizide and glimipiride); (4) incretin hormone mimetics (GLP-1 derivatives and analogs, such as exenatide and liraglitide); and (5) inhibitors of incretin hormone degradation (DPP-4 inhibitors, such as sitagliptin).
Many of the current treatments for diabetes have unwanted side effects. Phenformin and metformin can induce lactic acidosis, nausea/vomiting, and diarrhea. Metformin has a lower risk of side effects than phenformin and is widely prescribed for the treatment of Type 2 diabetes. The currently marketed PPAR gamma agonists are modestly effective in reducing plasma glucose and hemoglobin A1C, and do not greatly improve lipid metabolism or the lipid profile. Sulfonylureas and related insulin secretagogues can cause insulin secretion even if the glucose level is low, resulting in hypoglycemia, which can be fatal in severe cases. The administration of insulin secretagogues must therefore be carefully controlled. There remains a need for treatments for diabetes that work by novel mechanisms of action and that exhibit fewer side effects.
AMP-activated protein kinase (AMPK) has been identified as a regulator of carbohydrate and fatty acid metabolism that helps maintain energy balance in response to environmental and nutritional stress. There is evidence that activation of AMPK results in a number of beneficial effects on lipid and glucose metabolism by reducing glucogenesis and de novo lipogenesis (fatty acid and cholesterol synthesis), and by increasing fatty acid oxidation and skeletal muscle glucose uptake. Inhibition of ACC, by phosphorylation by AMPK, leads to a decrease in fatty acid synthesis and to an increase in fatty acid oxidation, while inhibition of HMG-CoA reductase, by phosphorylation by AMPK, leads to a decrease in cholesterol synthesis (Carling, D. et. al., FEBS Letters 223:217 (1987)).
In the liver, AMPK activation results in a decrease in fatty acid and cholesterol synthesis, inhibiting hepatic glucose production and increasing fatty acid oxidation. It has been shown that AMP-activated protein kinase regulates triacylglycerol synthesis and fatty acid oxidation in liver and muscle via glycerol-3-phosphate acyltransferase (Muoio, D. M. et. al., Biochem. J. 338:783 (1999)). Another substrace of AMPK, hepatocyte nuclear factor-4α, has been shown to be involved in type-1 maturity onset diabetes (Leclerc, I. et. al., Diabetes 50:1515 (2001)). Additional processes believed to be regulated through AMPK activation include the stimulation of glucose transport in skeletal muscle and the regulation of key genes in fatty acid and glucose metabolism in the liver (Hardie, D. G. and Hawley, S. A., Bioessays 23: 1112 (2001), Kemp, B. E. et al., Biochem. Soc. Transactions 31:162 (2003), Musi, N. and Goodyear, L. J. Current Drug Targets-Immune, Endocrine and Metabolic Disorders 2:119 (2002); Lochhead, P. A. et. al., Diabetes 49:896 (2000); and Zhou, G. et. al., J. of Clin. Invest. 108: 1167 (2001).
In vivo studies have demonstrated the following beneficial effects of both acute and chronic administration of AICAR, an AMPK activator, in rodent models of obesity and type 2 diabetes: 1) an improvement in glucose homeostasis in insulin-resistant diabetic (ob/ob) mice; 2) a decrease in blood glucose concentrations in ob/ob and db/db mice and a blood glucose reduction of 35% following 8 weeks of administration; and 3) a reduction in metabolic disturbances and a reduction of blood pressure in rats displaying characteristics of insulin resistance syndrome (Bergeron, R. et. al., Diabetes 50:1076 (2001); Song, S. M. et. al., Diabetologia 45:56 (2002); Halseth, A. E. et al., Biochem. and Biophys. Res. Comm. 294:798 (2002); and Buhl, E. S. et al., Diabetes 51: 2199 (2002)). A further study of 7 week AICAR administration in obese Zucker (fa/fa) rats lead to a reduction in plasma triglycerides and free fatty acids; an increase in HDL cholesterol; and a normalization of glucose metabolism as assessed by an oral glucose tolerance test (Minokoshi, Y. et. al., Nature 415: 339 (2002)). Expression of dominant negative AMPK in skeletal muscle of transgenic mice has demonstrated that the AICAR effect on stimulation of glucose transport is dependent on AMPK activation (Mu, J. et. al., Molecular Cell 7: 1085 (2001)).
Recent data also suggest that AMPK activation is involved in the glucose and lipid-lowering effects of the anti-diabetic drug metformin. It has been shown that the diabetes drug metformin can activate AMPK in vivo at high concentrations (Zhou, G. et. al., J. of Clin. Invest. 108: 1167 (2001); Musi, N. et. al. Diabetes 51: 2074 (2002)).
Based on these studies, it is expected that the in vivo activation of AMPK in the liver may result in the reduction of hepatic glucose output, an improvement in overall glucose homeostasis, a decrease in fatty acid and cholesterol synthesis, and an increase in fatty acid oxidation. Stimulation of AMPK in skeletal muscle is expected to result in an increase in glucose uptake and fatty acid oxidation with resulting improvement of glucose homeostasis, and an improvement in insulin action. Finally, the resulting increase in energy expenditure should lead to a decrease in body weight. The lowering of blood pressure has also been reported to be a consequence of AMPK activation.
Increased fatty acid synthesis is a characteristic of many tumor cells, therefore decreasing the synthesis of fatty acids via AMPK activation may also be useful as a cancer therapy. Activation of AMPK may also be useful to treat ischemic events in the brain (Blazquez, C. et. al., J. Neurochem. 73: 1674 (1999)); to prevent damage from reactive oxygen species (Zhou, M. et. al., Am. J. Physiol. Endocrinol. Metab. 279: E622 (2000)); and to improve local circulatory systems (Chen, Z.-P., et. al. AMP-activated protein kinase phosphorylation of endothelial NO synthase. FEBS Letters 443: 285 (1999)).
Compounds that activate AMPK are expected to be useful to treat type 2 diabetes mellitus, obesity, hypertension, dyslipidemia, cancer, and metabolic syndrome, as well as cardiovascular diseases, such as myocardial infarction and stroke, by improving glucose and lipid metabolism and by reducing body weight. There is a need for potent AMPK activators that have pharmacokinetic and pharmacodynamic properties suitable for use as human pharmaceuticals.
Benzimidazole compounds are disclosed in WO 93/07124; WO 95/29897; WO 98/39342; WO 98/39343; WO 00/14095; WO 00/03997; WO 01/53272; WO 01/53291; WO 02/092575; WO 02/40019; WO 03/018061; WO 05/002520; WO 05/018672; WO 06/094209; U.S. Pat. No. 6,312,662; U.S. Pat. No. 6,489,476; US 2005/0148643; DE 3 316 095; JP 6 298 731; EP 0 126 030; EP 0 128 862; EP 0 129 506; and EP 0 120 403. AMPK activators are disclosed in WO 08/006,432; WO 05/051298; WO 05/020892; US 2007/015665; US 2007/032529; US 2006/287356; and US 2005/038068.